The present invention relates to a transport device for transporting an original to be copied, while resting on a support surface, through the processing stations of a reproducing or copying machine, the transport device comprising gripping elements spaced across the width of the support surface and holding the leading edge of the original during transport.
In copying and reproducing machines several devices are already known for holding the leading edge of a moving original. For example, in German Offenlegungsschrift No. 2,026,063 a drum of a copying machine is described which is provided with a number of projecting grippers arranged across the surface of the drum and clamping the leading edge of an original to be copied. Each gripper is fastened in the drum by means of locking blocks accommodating an operating rod for actuating the grippers. For this purpose, the insides of the grippers at their bases each interact with a respective flattened portion of the operating rod. When the rod is turned clockwise, the grippers are withdrawn from the surface of the drum against the action of a spring which normally presses the grippers onto the surface of the drum and it is thus possible to place on or remove from the drum an original to be copied. In this known device each gripper is individually mounted in the drum, and consequently the gripping device is technically complicated and expensive.
From German Offenlegungsschrift No. 2,365,228 a gripping device is known which comprises a clamping bar provided with a number of grippers. This clamping bar is arranged inside of a drum in a radial slot, and in order to clamp the paper original inserted into the slot, the clamping bar is pressed onto a clamping surface inside the drum by means of a lever arrangement actuated by an electromagnet having an armature. When the clamping bar is opened, the grippers slightly project beyond the surface of the drum, so that an original can be placed underneath them. In this known gripping device having a rigid clamping bar, difficulties arise, inter alia, due to the fact that it is not possible to compensate for varying thicknesses at the margins of an original to be copied across its width. As a result, the entire clamping force of the clamping bar, at best, acts upon the margins on the right and on the left of the original, but not in between, since in this area the clamping bar does not rest upon the original. As is known from experience, the major clamping force of such a clamping bar is exerted at the point of maximum thickness of the original, and due to the unequal clamping force across the width of the original, the latter may tear, slip, bulge or be destroyed during transport. Since the control means for opening and closing this known gripping device is positioned outside the drum, additional room is required, a fact which precludes the desired compact design in reproducing and photocopying machines.
A known gripping device described in German Offenlegungsschrift No. 2,343,133 is mounted on an endless transport system, e.g., formed by two chains, and comprises a metal gripping frame attached to the transport chains, movable metal clamps, and pads which are to avoid any scratching or other damaging of the photoconductive drum when the gripping device approaches the drum. In this case, the gripping device does not rotate with the photoconductive drum, but only leads the copying material, onto which the developed powder image is to be transferred, past the transfer station of the photoconductive drum. The movable clamps are prestressed by springs and are opened by rigid pins in such a way that they are lifted off from a stationary clamp of the metal gripping frame.
Although the known gripping devices, either consisting of a drum with individual mounted grippers or of a rigid clamping bar extending across the surface of the drum, accomplish their task of conveying the originals to be copied, it is difficult, with those devices, to make copies of originals which have slightly damaged leading edges or which vary in thickness across their width, as for instance originals provided with a suspension strip on one side, which strip is normally much thicker than the original to be copied.
The known gripping system with individually mounted flexible grippers seizes the leading edge of an original to be copied in predetermined areas and exerts a largely uniform grip force. It is also suited for originals with suspension strips of different thicknesses, but it has the disadvantage that the leading edge of the original is not covered over its entire width. It is, however, necessary to cover the entire leading edge of an original, when the leading edge is damaged, e.g., when it is torn or deformed. During transport of the original to be copied through a copying or reproducing machine, especially when further rolls, webs and similar transporting elements pass over its leading edge, such damage may be aggravated or the original may even be destroyed. This may happen in particular when the original is transported through the machine several times for repeated copying.
A gripping system comprising a rigid clamping bar covers and protects the entire leading edge of the original; however, it is not able to compensate for a differing thickness across the leading edge of the original caused by the difference in gauge between paper and suspension strip. Thus, the clamping bar exerts a non-uniform clamping force across the width of the leading edge. As mentioned before, tearing, slipping, bulging or other damaging of the original to be copied may result.
The control systems incorporated in the known gripping devices either deviate each gripper individually and in parallel with the other grippers in the gripping system, or they displace a clamping bar with respect to a clamping surface inside of a drum.